System and Method for Photonic Switching

ABSTRACT

In one embodiment, method of wrapping photonic packets includes receiving, by a node, a first packet and receiving, by the node, a second packet. The method also includes concatenating the first packet and the second packet to produce a concatenated frame, where concatenating the first packet and the second packet includes removing an inter-packet-gap (IPG) between the first packet and the second packet and converting the concatenated frame to a photonic frame, where the concatenated frame is an electrical frame.

This application claims the benefit of U.S. Provisional Application Ser.No. 61/822,147 filed on May 10, 2013, and entitled “System and Methodfor Wrapping Photonic Packets,” which application is hereby incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a system and method for opticalcommunications, and, in particular, to a system and method for photonicswitching.

BACKGROUND

Growth of internet traffic, fueled by the growth in the number of usersand by increasing numbers of applications, results in a higher demandfor bandwidth. This growth entails larger packet networks with greaterswitching capabilities. Data centers contain huge numbers of racks ofservers, racks of storage devices, and other racks, all of which areinterconnected via a massive centralized packet switching resource. Indata centers, electrical packet switches are used to route data packets.Electronic packet switching at very high rates involves massive coolingand space costs. Thus, photonic packet switching is desirable.

The racks of servers, storage, and input-output functions contain top ofrack (TOR) switches which combine packet streams from their associatedservers and/or other peripherals into a smaller number of high speedstreams per TOR which are routed to the packet switching core. Also,TORs receive the returning switched streams from that resource anddistribute them to servers within their rack. There may be 4×40 Gb/sstreams from each TOR to the packet switching core, and the same numberof return streams. There may be one TOR per rack, with hundreds to tensof thousands of racks, and hence hundreds to tens of thousands of TORsin a data center.

SUMMARY

An embodiment method of wrapping photonic packets includes receiving, bya node, a first packet and receiving, by the node, a second packet. Themethod also includes concatenating the first packet and the secondpacket to produce a concatenated frame, where concatenating the firstpacket and the second packet includes removing an inter-packet-gap (IPG)between the first packet and the second packet and converting theconcatenated frame to a photonic frame, where the concatenated frame isan electrical frame.

An embodiment method of switching wrapped photonic frames includesreceiving, by a photonic switching fabric from a first node, a firstwrapped photonic frame and determining a destination address of thefirst wrapped photonic frame. The method also includes setting up aconnection in a photonic switch during a gap time between the firstwrapped photonic frame and a second wrapped photonic frame and switchingthe first wrapped photonic frame after setting up the connection in thephotonic switch.

An embodiment method of unwrapping wrapped photonic frames includesreceiving, by a node, a wrapped photonic frame and unwrapping thewrapped photonic frame to produce a first packet and a second packet,including adding an inter-packet-gap (IPG) between the first packet andthe second packet. The method also includes directing the first packetto a destination.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a packet stream;

FIGS. 2A-B illustrate embodiment wrapped photonic frames;

FIG. 3 illustrates the wrapping of a packet stream between a source anddestination into a wrapped photonic frame;

FIG. 4 illustrates an embodiment system for wrapping and switchingphotonic packets;

FIG. 5 illustrates the wrapping of another packet stream to a wrappedphotonic frame;

FIG. 6 illustrates another embodiment wrapped photonic frame;

FIG. 7 illustrates an embodiment system for wrapping packets insynchronous time slot systems;

FIGS. 8A-D illustrate waveforms, an eye diagram, and a wrapped photonicpacket for wrapping and switching photonic packets;

FIG. 9 illustrates an embodiment photonic switching system with softwaredefined networking (SDN);

FIG. 10 illustrates an embodiment photonic switching fabric;

FIG. 11 illustrates an embodiment system for switching photonic packets;

FIG. 12 illustrates an additional embodiment system for wrappingphotonic packets;

FIG. 13 illustrates an embodiment star architecture;

FIG. 14 illustrates an embodiment ring architecture;

FIG. 15 illustrate an embodiment system for wrapper photonic frames in acentralized photonic switching fabric;

FIG. 16 illustrates a flowchart for an embodiment method of wrappingpackets;

FIG. 17 illustrates a flowchart for an embodiment method of switchingwrapped photonic frames; and

FIG. 18 illustrates a flowchart for an embodiment method of unwrappingpackets.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

In an optical space switch, a photonic connection from one physical portto another lasts for the duration of a packet or frame, and is changedbetween packets or frames. Increasing data rates lead to even smallerswitching windows. Some photonic switches have switching times of tensof nanoseconds. FIG. 1 illustrates an example packet stream, packetstream 100, which contains data regions 102, header regions 104, andinter-packet gaps (IPGs) 106 between packets. There are a fixed numberof bits in the IPG. In one example, the IPG is 96 bits. For a fixednumber of bits, the length of time of the IPG inversely depends on thelink rate. For example, a 96 bit IPG is 10 ns at 10 Gb/s, 2.5 ns at 40Gb/s, 1 ns for 100 Gb/s, and 0.08 ns for 1.28 Tb/s.

An embodiment wrapper and addressing scheme for top-of-rack (TOR) to TORor TOR group to TOR group communications within a data center wrapspackets in a photonic frame. The wrapping scheme is independent of theswitching architecture and may be used in both centralized and/ordistributed photonic switching architectures. Buffering occurs in theTOR or TOR group in the electrical domain instead of in the opticaldomain. A routing table of the network addresses other TORs or TORgroups within the data center may be used to wrap packets together whichhave the same destination.

Packet wrapping may be used in a variety of photonic switchingconfigurations. A photonic switching system may be centralized ordistributed. Also, it may be a synchronous or asynchronous system. In anasynchronous system, packets are sent to their destination in a burst,while in a synchronous system, like optical time division multiplexing(OTDM), packets are sent to their destination in a designated timeslot.The functions of wrapping and unwrapping packets may be performed by anode, such as a TOR or TOR group, or by a standalone device, such as afield programmable gate array (FPGA) or by an access or edge node. In anembodiment, wrapped packets are grouped by their destination address fora scalable solution, because the label of a photonic switch isassociated with the network hierarchy address of a data center. Anembodiment wrapper scheme removes the IPG between individual packets byconcatenating packets to form wrapped photonic frames and inserting anappropriate gap time between the wrapped photonic frames. This gap timemay be used to set up a photonic switch for switching the photonicframes. In one example, packets belonging to a group address with aparticular label based on an addressing scheme are wrapped together.Alternatively, packets are grouped in another way. For example, packetswhich arrive consecutively from the same TOR or TOR groups are groupedtogether. In one example, a gap time of 201 ns is used, and 20 packetsare in a wrapped packet at a data rate of 10G. In this example, thecontrol time is 101 ns, the switching time is 40 ns, and the clock anddata recovery (CDR) time is 60 ns. For a link rate of 100 Gb/s with 32packets wrapped in a photonic frame, with an IPG of 12 bytes, the sum ofthe IPGs is 384 bytes, which is equal to the gap time, about 30 ns. Theinserted gap has a low overhead, because the IPGs are removed.

FIGS. 2A-B illustrate examples of wrapped photonic frames. In FIG. 2A,wrapped photonic frame 140 contains data regions 102 and header regions104 concatenated together. Gap 142 is disposed between wrapped photonicframes. Label 144 identifies the wrap and sent over an out-of-band labelat a different wavelength than the traffic wavelength, arrives atdestination during gap 142. In one example, label 144 is a wavelengthencoded address. The headers for the individual packets are similar tothose in unwrapped packets. In this example, the time between packets isthe gap time, given by:

GAP=Σ_(i)IPG_(i).

In another example illustrated by FIG. 2B, wrapped photonic frame 150contains data regions 102 and header regions 104 concatenated together.Label 152 and gap 154 are between the wrapped frames. Label 152 is sentin-band, and the time between wrapped packets is the sum of the time ofthe gap and the label, which is given by:

GAP+Label=Σ_(i)IPG_(i).

In an example addressing scheme, a group of TORs belonging to a networkaddress, for example a subnet or super virtual local area network (VLAN)are associated with a single address. The packets destined to aparticular TOR group are wrapped and assigned an optical addressindicating the destination TOR group.

In another example, packet concatenation for packets at either theinternet protocol (IP) or the link layer of the transmission controlprotocol (TCP)/IP is used. This may be used for high rates, such as 1.28Tb/s. FIG. 3 illustrates packet concatenation into a single link layerpacket where the payload size is larger than 1500 bytes. Link layer 464contains physical layer (PHY) header 480, link layer (LL) header 482,payload 484, and frame check sequence (FSC) 486, while IP layer 462contains PHY header 466, LL header 468, IP packet 470, and FSC 478. IPpacket 470 contains IP header 472, TCP header 474, and application data476. Multiple of IP packets 470 are placed in payload 484, PHY headers466 are placed in PHY header 480, LL headers 468 go to LL header 482,and FSCs 478 go to FSC 486 in link layer 464. Payload 484 is larger thana maximum transmission unit (MTU) of 1500 bytes.

FIG. 4 illustrates system 200 for a single core switch data center.Servers 202 and clients 204 are coupled to wrapper blocks 206. Aspictured wrapper blocks 206 contain TOR 208 and FPGA 210, whichimplements photonic frame wrapping. In another example, the photonicframe wrapping is implemented in the TOR, and not as a separate device.The photonic wrapping may be integrated in the TOR without externalelectronic circuit.

The wrapped frames are passed to photonic switch 214, for example alongoptical fibers. In one example, the photonic switch is a lead zirconiumtitanate (PLZT) photonic switch. In another example, the photonic switchis a silicon photonic (SiP) photonic switching fabric.

A portion of the output is tapped off to controller 216. The controllermay be, for example, implemented in an FPGA switch controller. Thecontroller implements synchronization and signaling and controls thephotonic switch using control signals. In another example, thecontroller is embedded in the photonic switching fabric.

FIG. 5 illustrates an embodiment frame wrapping technique. Packets 220contain media access control (MAC) frame 222, preamble 224, and IPG 226.The preamble, which is 7 bytes, performs synchronization. Wrapped packet228 contains idle period 230, MAC frame 232, frame length 234, preamble236, MAC frame 238, frame length 240, preamble 242, start framedelimiter (SFD) 244, gap 248, and label 250. Multiple packets areconcatenated in a single wrapped frame. The IPGs between the packets areremoved, and a gap and label are placed between the wrapped frames.

FIG. 6 illustrates an example of a wrapped photonic frame in asynchronous slotted system. The wrapper time slot is 6328 clock cycles.The label contains destination address (DA) 294 and SFD 292. Gap 296 is31 clock cycles. There is idle period 300, length of frame (len_f) 302,preamble 304, and MAC frame 306, which constitute the retransmit patternof other MAC frames in the wrapper before the clock cycle of wrappertime slot is exhausted. Len_f indicates the number of bytes in theframe, for use in determining whether there is an error. After theretransmit pattern is idle period 308, len_f 310, preamble 312, MACframe 314, and idle period 316.

FIG. 7 illustrates system 270 for wrapping packets. System 270 is a 4×4exchange, with four timeslots in each lane. In this example, wrapping isperformed synchronously. Initially, unwrapped packets are received byinput block 272. Input block 272 reads the destination address of thepacket and routes the packet to the correct buffer for that destinationaddress.

The unwrapped packets proceed to wrapper blocks 274. In wrapper blocks274, the unwrapped packets are separated by destination. For example,unwrapped packets may be separated by destination TOR group ordestination TOR. The separated packets are placed in buffers 276. Thereis a separate buffer for each destination. Then, packets 276 from thebuffers are read out and wrapped by wrappers 284. This is coordinated bysynchronization block 286. A synchronization signal from synchronizationblock 286 indicates that the wrapped packets are synchronously read outfrom wrappers 284. The wrapping and transmission of the packets arestaggered to avoid contention. For example, of the four wrappers 284,one outputs a wrapped photonic frame for output 3, one outputs a wrappedphotonic frame for output 4, one outputs a wrapped photonic frame foroutput 1, and one outputs a wrapped photonic frame for output 2.

The wrapped frames are then transmitted by output block 288 to be sentfor photonic switching. Block 288 are transceivers which convertelectrical signals to optical signals.

FIGS. 8A-D illustrate results using a photonic frame wrappingimplemented by emulating a wrapped frame with one packet per frame. Aserver sends Ethernet frames with four different destination MACaddresses, each destined to a different photonic output port of aphotonic switch. FIG. 8A illustrates graph 310 with the frame waveformon the four output ports of the photonic switch. The photo-receivervoltage polarity is inverted, with horizontal lines when there is nolight and the waveforms when there are switched frames.

FIG. 8B illustrates wrapped photonic frame 320. Photonic frame 320contains label 322, which is 8 bytes, gap and preamble 324, which is 176bytes, SFD 326, and MAC frame 328, which is 1470 bytes. Label 322indicates the destination address. Gap and preamble 324 contains the gapfor photonic switching and the preamble. SFD 326 is used to detecterrors.

FIG. 8C illustrates a graph with a detailed output frame waveform of twooutput ports of a photonic switch. Curve 341 shows the completion of aphotonic frame transmission, and curve 343 starts sending a preamble andphotonic label. Time t0 represents the total time for the label, gap,preamble, and SFD. Time t1 represents the earliest time that the processof a label can be started before frame transmission is completed. Timet1 is 106.9 ns, the switch response time t2 is 12 ns, residual preamblefor receiver synchronization is 15 ns, the preamble for CDR, t3, is 13ns, and the SFD time is 12 ns.

FIG. 8D illustrates graph 330 with an eye diagram of the switchedsignal. Because the total processing time is 130 ns, the latency forcontrol processing is approximately 130 ns minus the switch responsetime minus the residual preamble time, or 103 ns. This delay can becompensated for by a 21 m fiber delay line inserted between tappedcontrol signal and photonic switch.

FIG. 9 illustrates system 351, a memory-less optical data plane withsoftware defined networking (SDN) for photonic frame switching. System351 has an edge buffer architecture. Routers 359 are coupled to accessnetworks 355. Routers 359 pass packets to photonic switching core 357for switching.

SDN controller 353 may be used for source based routing. SDN controller353 facilitates programmable control of photonic packet switchingwithout physical access to the photonic switches.

Photonic switching core 357 contains wrappers 361, which wrap packets toproduce wrapped photonic frames. Wrappers 361 remove the IPG betweenpackets and concatenate the packets, creating gaps between photonicframes. The gap may be about equal to the sum of the removed IPGs.

During the gaps between photonic frames, photonic switches 363 switchthe wrapped photonic frames. Photonic switches 362 may be implemented asPICs. In one example, photonic switches are dilated SiP photonicswitches with asynchronous contention control. An example photonicswitching fabric is illustrated by FIG. 10, which shows photonicswitching system 180, which resolves contention using deflection. InputTORs (switches or routers) 182 transmit photonic frames to photonicswitching fabric 184.

Load balancing is performed by load balancing block 198. Load balancingequally utilizes the output ports to prevent lost packets. The loadbalancer and SDN work together to perform load balancing. When loadbalancing is effective, the inputs and outputs have a similar trafficdistribution.

A header is sent by the source TORs in advance of the frame. In oneexample, the header indicates the first three choices of destinationport. The label is read by label detectors 188. In one example, thedestination address is wavelength encoded, where each wavelengthindicates a bit for the destination address. The wavelengths have twopower levels. Low power may represent a 0 and high power a 1, or viceversa.

The destination address is passed to switch controller 190. Switchcontroller 190 performs contention analysis and scheduling. In oneexample, three preferred output ports are sent to switch controller 190.Switch controller 190 determines which of the requested destinationports are available. The highest priority available destination port isapproved. It is possible, but unlikely, that none of the choices areavailable. In this case, the wrapper is lost.

When a frame is received by photonic switching fabric 184, it is routedby photonic switches 186, 2×3 photonic switches which route the packetto the appropriate input of photonic switch 192, photonic switch 194, orphotonic switch 196. Photonic switches 192, 194, and 196 may be dilatedSiP photonic switches with many 32×32 silicon photonic switchingfabrics. The photonic frame is then switched to the appropriate outputport, and output to output TORs (or routers) 185. The frame is switchedbased on the decision by switch controller 190.

More details on asynchronous contention control are discussed in U.S.Patent Application HW 81092777US02 filed on May 12, 2014, and entitled“System and Method for Photonic Switching,” which application is herebyincorporated herein by reference.

FIG. 11 illustrates system 430, an architecture for wrapping packets forcentralized photonic switching in a data center. A TOR group (TG) hasmany hosts and servers which are part of the same group address. A TORgroup may be a multiplexer/demultiplexer group or a mapper/de-mapperbuilt into an application specific integrated circuit (ASIC), or an FPGAwhich wraps the packets on the transmission side and unwraps the packetson the receiving side. Alternatively, a TOR group is a packet switchwith integrated wrapping and unwrapping functions. A TOR group isconnected to multiple TORs, and a TOR is connected to multiple servers.In one example there are, 32 TOR groups, each TOR group has 32 TORs, andeach TOR is attached to 48 servers. In this example, there are 49,152servers.

A TOR group belongs to a group address. In one example, there is anetwork address of 192.10.x.x/16. In this example, TOR group 1 coversnetwork addresses from 192.10.0.0 to 192.10.7.255, TOR group 2 coversnetwork addresses from 192.108.0.0 to 192.10.247.255, . . . , and TORgroup 32 covers network addresses from 192.10.248.0.0 to 192.10.255.255.Thus, there are a total of 2048 servers in the TOR group.

Traffic from the hosts or servers of a TOR group destined for other TORgroups passes through a TOR group address filter (TAF). The TOR grouplooks at the destination of an IP address and determines which TOR groupit belongs to by applying the address to a set of masks. In one example,the subnet address of the destination address is obtained by performinga logical AND of the IP address with a subnet or super-subnet mask.

TOR group D 432 wraps packets into wrapped photonic frames. To wrappackets, packets with the same destination are concatenated with theIPGs removed and wrapped into a frame. For example, wrapped photonicframe 434 contains packets 438 destined for TOR group A 454 with label436 indicating this destination. Similarly, wrapped photonic frame 442contains packets 446 destined for TOR group AF 455 and label 444indicating this destination. Between wrapped photonic frame 434 andwrapped photonic frame 442 is gap 440.

Photonic switching fabric 448 switches the wrapped photonic packets.Photonic switching fabric 448 sets up the connections during the gaptime between frames for the next frame. Photonic switching fabric 448directs wrapped photonic frame 450 to TOR group A 454 and directswrapped photonic frame 451 to TOR group AF 455. Photonic switchingfabric 448 detects the label, routes the photonic frame to thedesignated output, and removes the labels.

TOR group A 454 and TOR group AF 455 receive wrapped photonic frames,unwrap then, direct them to the appropriate TOR of TORs 456. In oneexample, a TOR group has 32 TORs. The TORs then direct the packets tonetworks 458.

FIG. 12 illustrates wrapper 371 for wrapping packets. In one example,wrapper 371 is a part of a TOR or a TOR group, such as TOR group D 432.Incoming packets 373 are destined for TOR groups. Block 375 receives thepackets, performs address filtering and output queuing. Packets arefiltered by destination address, for example by destination TOR ordestination TOR group. The IP address is examined and mapped to a TORgroup address, for example based on the destination TOR's subnetaddress. Packets are separated, for example based on the destination TORgroup. The separated packets are placed in the appropriate queue ofbuffers 377. One queue contains packets for destination TOR group A,another queue contains packets for destination group B, etc.

Block 379 performs wrapping, scrambling, and wavelength encoding. Whenthe traffic length for a queue has reached a certain sized, for examplebased on a defined wrap size, or the delay jitter budget for holding thepacket at the head of the queue has been reached, the packets in a queueare concatenated, and an optical label is inserted. When the wrap sizehas not been reached, dummy packets may be added. A label is added to awrapped photonic packet. The label may be converted from the networkaddress. The wrapper may also be scrambled. Use of 64B/66B encoding(scrambling) schemes for photonic switching may cause severe bit errorrate. This is because, unlike electronic packet switches, photonicpacket switches lack electrical transceivers to maintain bit streamcontinuity on each their outputs. As a result, to ensure clock recoveryat the receiver, a frame-based scrambling may be deployed for photonicwrappers. The scrambler may be 2¹⁶−1 pseudorandom binary sequence (PRBS)generator. The wrapped packets are converted from the electrical domainto the photonic domain. Additionally, a wavelength encoded label isadded to the wrapped photonic packet. In one example, the destinationaddress is wavelength encoded, and each wavelength indicates a bit forthe destination address. The wavelengths have two power levels. Lowpower may represent a 0 and high power a 1, or vice versa. More detailson wavelength encoding are discussed in U.S. patent application Ser. No.13/902,085 filed on May 24, 2013, and entitled “System and Method forMulti-Wavelength Encoding,” which application is hereby incorporatedherein by reference.

Wrapped photonic frames 381 and 388, in the photonic domain, containpackets 384 and 393 and labels 383 and 391. The routing labels arewavelength encoded. Gap 387 lies between wrapped photonic frame 381 andwrapped photonic frame 388. In one example, the gap time is from about10 ns to about 30 ns. In another example, gap time is engineered (forexample by increasing the number of packets in a wrap) to absorb thephotonic processing delays.

An architecture which may be used for centralized photonic switching issystem 120 illustrated in FIG. 13. Photonic switching fabric 122connects TORs or TOR groups 126 in a star configuration. The TORs or TORgroups are assigned a group address. TORs or TOR groups 126 areconnected to subnets 124. In an example, a packet wrapping scheme with afixed wrapper size is used. A TOR group encodes the destination TORgroup address into an optical label associated with that address.Broadcast and multicast of the traffic are performed with a TAF, wherethe packet is replicated to the destination addresses which belong to amember of a multicast group. In multicasting, multiple copies of thetraffic are provided at a packet level to destination TOR groups.

In another example, illustrated by system 130 in FIG. 14, a ringarchitecture is used. Photonic switching may be synchronous orasynchronous. TORs 134 are connected to each other in a ring by highcapacity photonic ring 132. Also, TORs 134 are connected to subnets 136,which are clouds. In one example, high capacity photonic ring 132 has abandwidth of 1.28 Tbps. For example, high capacity photonic ring 132 maybe stacks of rings, where each ring has a rate of 100 Gbps, 200 Gbps, or400 Gbps. Each node, for example a TOR or TOR group, inserts its wrappedtraffic when it sees an empty photonic label. The node inserts the wrapand replaces the empty optical label with a wrap destination.

The nodes use a network address which is mapped to an optical label. Thesignaling waveband carries both routing and management information.Because the number of nodes in a ring is limited, a limited number ofwavelengths may be used for addressing the TORs. For example, assumingtransceivers operate in 12 wavelengths in the 1550 nm range, some of thewavelengths may be used to address ring nodes and some are used formanagement and control. The signaling waveband may also carry othercontrol signals, such as congestion status, fairness, and management. Inone example, an asynchronous mode of operation is used for photonic ring132. In the asynchronous mode, the gap may be fixed to the time forperforming switching and control. However, wrap size could vary. Inanother example, OTDM and synchronous mapping are used.

In a synchronous example, there is one wrap in each time slot, where thewrap time is fixed and equal to the slot time. The gap time is used toconfigure the photonic switch. The node determines whether a frame isdestined for that node. When the frame is destined for that node, thenode takes the frame and unwraps it. When the node is not destined forthat node, the packet continues around the ring.

FIG. 15 illustrates system 340, an embodiment photonic switching systemthat uses optical space switching. System 340 is a bufferless photonicswitch which uses a photonic wrapper. Separate wavebands are used forthe control signal path and the payload data path. Photonic routinglabels are used on the forward path between TORs (or switches) and thephotonic switch. Signaling on the return path (between photonic switchand TORs) is used for contention control and synchronization.

Server network 342 is simulated by simulator 344 and simulator 346.Simulators 344 and 346 contain small form factor pluggable transceivers(SFPs) 348, 350, 352, and 354, which are connected to TORs 356, 358,360, and 362. The signals are sent to FPGA 366.

In FPGA 366, signals are received by SFP 368. These signals are proceedby front-end adaptor 372. Labels are generated by label generator 374.The signals and groups are output by SFP 378 to photonic switchingfabric 386 and FPGA 390.

The optical signal of the labels is converted to an electrical signal byoptical-to-electrical converters 398, and is received by FPGA 390. Theyare processed by processor 396. Then, the control signal is extracted bycontrol signal extractor 394. The control signals are then converted bylow-voltage differential signal (LVDS) to transistor-transistor logic(TTL) board 392.

The data wave path signals and the signaling wave path signals aremultiplexed by multiplexer 380, with data at 40GE and signaling at 10GE,and output to photonic switching fabric 386. The control signals fromFPGA 390 are also input to photonic switching fabric 386. Photonicswitching fabric 386 is a 4×4 optical space switch which operates on adedicated waveband. The signals are switched, and output to FPGA 366.

The signals are received by demultiplexer 382 and SFP 378. They areprocessed by back-end adaptor 376. The signals are converted by FPGAmezzanine card (FMC) to subminiature version A (SMA) converter 370. Thesignals are converted to optical signals by electrical-to-opticalconverters 364, and proceed to TORs 356, 358, 360, and 362.

FIG. 16 illustrates flowchart 490 for a method of wrapping photonicpackets. Initially, in step 492, packets are received by a node, forexample a TOR or TOR group. The packets may be received form a server ornetwork. The received packets are in the electrical domain, with an IPGbetween packets, for example in an IP format.

Next, in step 494, the packets are separated into queues. In oneexample, packets are separated by destination TOR or TOR group. Packetsare directed to one of several buffers corresponding to the destination.In another example, packets are placed in a buffer based on the paththey travel, e.g., source based routes.

In step 496, the packets are concatenated. When a buffer is full, or amaximum period of time has passed, the packets are read out of thebuffer. If the buffer is not full, padding may be added so the wrappedpackets are of a uniform length. There is no IPG between the packetswhen they are read out of the buffer. After a wrapped photonic frame isread out of one buffer, the next wrapped photonic packet is read out ofanother buffer after a gap time. The gap time may be the sum of the IPGswhich have been removed. In one example, it is from about 10 ns to about30 ns. The gap time may be chosen based on the time to set up thephotonic switch, and the time for the switching function.

Then, in step 498, the wrapped frame is converted from the electricaldomain to the optical domain. This may be done usingelectrical-to-optical converters. A designated traffic wavelength may beused.

A label is added to the wrapped photonic packet in step 500. In oneexample, the label is added in the same wavelength as the trafficwavelength. In this case, the label may be added before the gap.Alternatively, the label is added at a different wavelength than thetraffic wavelength. For example, the label may be wavelength encoded,where the presence or absence of light is a wavelength indicates anaddress bit.

Finally, in step 502, the wrapped photonic frame is transmitted to aphotonic switch. This may be done along an optical fiber.

FIG. 17 illustrates flowchart 510 for a method of switching wrappedphotonic frames. Initially, in step 512, a photonic switching fabricreceives a wrapped photonic frame from a node. The photonic switchingfabric may contain an optical photonic switch.

In step 514, the photonic switching fabric decodes the label to obtaindestination address for the wrapped photonic frame. In one example, theaddress indicates the destination node for the wrapped photonic frame.In one example, the address is decoded as ones or zeroes based on thepresence or absence of light in the timeslot. Alternatively, the addressis wavelength encoded. To decode a wavelength encoded address,wavelengths are separated, and the presence or absence of light isdetected, to indicate address bits. In one example, in a ringconfiguration, the photonic switching fabric determines whether thewrapped photonic frame is destined for that node. When the wrappedphotonic frame is not destined for that node, it continues along thering. When the wrapped photonic frame is destined for that node, thephotonic switching fabric siphons it from the ring, and switches ittowards its destination.

Next, in step 516, the photonic switch is set up during the gap. Theconnections of the photonic switch are set up during the gap time basedon the destination address. In one example, the photonic switch is asilicon photonic switch.

Then, in step 518, contentions are resolved. Contentions may besynchronously resolved, for example using slotted system in whichcontending sources transmit in different time slots. Several choices ofoutput port may be considered. Then, the wrapped photonic frame isdirected to one of the available output port.

In step 520, the wrapped photonic frame is switched by the photonicswitch. Connections in the photonic switch are maintained for theduration of the photonic frame. After the photonic frame is switched,the photonic switch sets up for the next wrapped photonic frame duringthe next gap time.

Finally, in step 522, the photonic switch transmits the switched wrappedphotonic frame to a node. The wrapped photonic frame may be transmittedto a destination TOR or TOR group or to the next hop in the network. Itmay be transmitted along an optical fiber.

FIG. 18 illustrates flowchart 530 for a method of unwrapping a wrappedphotonic frame. Initially, in step 532, a node receives a wrappedphotonic frame from a photonic switching fabric. The node may be a TORor TOR group.

Next, in step 534, the node converts the wrapped photonic frame to theelectrical domain. This may be done by optical-to-electrical converters.

Then, in step 536, the IPGs are put back between the packets. This maybe done by reading the received frame into a buffer. Then, the packetsare read out from the buffer, with an IPG between the packets.

Finally, the packets are directed to their destinations in step 538. ATOR group may direct the packets to the appropriate TOR. A TOR maydirect the packets to the appropriate subnet or server.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method of wrapping photonic packets, the methodcomprising: receiving, by a node, a first packet; receiving, by thenode, a second packet; concatenating the first packet and the secondpacket to produce a concatenated frame, wherein concatenating the firstpacket and the second packet comprises removing an inter-packet-gap(IPG) between the first packet and the second packet; and converting theconcatenated frame to a photonic frame, wherein the concatenated frameis an electrical frame.
 2. The method of claim 1, further comprisingadding a label to the photonic frame to produce a wrapped photonicframe.
 3. The method of claim 2, wherein the photonic frame and thelabel are at a traffic wavelength.
 4. The method of claim 2, wherein thephotonic frame is at a traffic wavelength and the label is in a controlwaveband.
 5. The method of claim 4, wherein the label is wavelengthencoded.
 6. The method of claim 2, further comprising transmitting, bythe node to a photonic switch, the wrapped photonic frame.
 7. The methodof claim 1, wherein the node is a top-of-rack (TOR) switch.
 8. Themethod of claim 1, wherein the node is a switch or a router.
 9. Themethod of claim 1, wherein the node is a TOR group.
 10. The method ofclaim 1, further comprising: determining a first destination group ofthe first packet; determining a second destination group of the secondpacket; and determining whether the first destination group equals thesecond destination group, wherein concatenating the first packet and thesecond packet is performed when the first destination group equals thesecond destination group.
 11. The method of claim 10, wherein the firstdestination group indicates a destination TOR.
 12. The method of claim10, wherein the first destination group indicates a destination TORgroup.
 13. The method of claim 1, wherein concatenating the first packetand the second packet comprises: writing the first packet to a buffer;writing the second packet to the buffer; and reading out the buffer toproduce the concatenated frame.
 14. The method of claim 13, whereinreading out the buffer occurs when the buffer is full.
 15. The method ofclaim 13, wherein reading out the buffer occurs after a set period oftime from writing the first packet to the buffer.
 16. The method ofclaim 15, further comprising padding the packet from the buffer.
 17. Amethod of switching wrapped photonic frames, the method comprising:receiving, by a photonic switching fabric from a first node, a firstwrapped photonic frame; determining a destination address of the firstwrapped photonic frame; setting up a connection in a photonic switchduring a gap time between the first wrapped photonic frame and a secondwrapped photonic frame; and switching the first wrapped photonic frameafter setting up the connection in the photonic switch.
 18. The methodof claim 17, further comprising transmitting the first wrapped photonicframe to a second node in accordance with the destination address, afterswitching the first wrapped photonic frame.
 19. The method of claim 17,wherein determining the destination address comprises determining thedestination address in accordance with a wavelength encoded label of thefirst wrapped photonic frame.
 20. The method of claim 17, furthercomprising determining whether the destination address corresponds to asecond node associated with the photonic switching fabric, whereinswitching the wrapped photonic frame comprises: directing the firstwrapped photonic frame to the second node when the destination addressindicates the second node; and directing the wrapped photonic frame to athird node when the destination address does not indicate the secondnode.
 21. A method of unwrapping wrapped photonic frames, the methodcomprising: receiving, by a node, a wrapped photonic frame; unwrappingthe wrapped photonic frame to produce a first packet and a secondpacket, comprising adding an inter-packet-gap (IPG) between the firstpacket and the second packet; and directing the first packet to adestination.
 22. The method of claim 21, wherein directing the firstpacket to the destination comprises routing the first packet to asubnet.